This invention relates to a drive assembly. The assembly may be utilised to drive a flexible elongate member such as cable or the like. Another aspect of the invention may be utilised to drive a pulley or a ground engaging wheel of an aircraft. The invention also relates to a method of driving a flexible elongate member such as a cable or wheel.
The deployment, or veering, of cable from a winch drum is often achieved by applying a tension to the cable to draw it from the drum. In a number of applications this veering may be achieved by means of the load present on the cable, for example, in a towed sonar array as might be deployed from a submarine or ship, the array is deployed from a winding drum mounted on the vessel by means of the drag on the array created by the surrounding water. However, initially, when only a short length of cable is deployed, the drag may not be sufficient to veer the cable from the winding drum and to pull the cable over the various pulley wheels that are provided between the drum and the point where the cable passes from the vessel. Such initial tension may be provided by a cable drive assembly beyond the last pulley wheel on the vessel, as will be described below.
When hauling in or recovering a cable or sonar array the winch drum is rotated in the opposite direction. The drag experienced by the sonar array, which may be several hundred metres long, places a significant load on the array and thus a significant load on the winch drum. This load may be sufficient to crush and damage the coils of cable already present on the drum, and may make spooling of the cable onto the drum difficult. To avoid this difficulty, a cable drive assembly as mentioned above may be utilised to haul in or recover the cable and reduce the tension in the cable as it is wound onto the drum: the drive assembly hauls in a portion of the recovery load and the winch drum hauls in the remainder of the recovery load.
The cable drive assembly may be a pair of driven rollers to form a nip beyond the last pulley wheel on the vessel. However, the point loads created by such a nip may damage the cable. In other arrangements, pairs of opposed driven belts are utilised to apply tension to the cable. The belts are maintained in contact with the cable by pivotally mounted longitudinally extending low friction supports. The supports are biassed inwardly towards one another by springs. However, the cables, and in particular towed sonar arrays, may be xe2x80x9clumpyxe2x80x9d, that is the cables are not or a constant diameter, and the larger diameter portions are not accommodated easily by the supports; when the supports are pushed apart to allow the larger diameter portions to pass, the smaller diameter sections of cable will not be gripped by the belts and the larger diameter portions will experience significant point loads and may be subject to damage or accelerated wear.
An alternative arrangement for handling cable is described in U.S. Pat. No. 3,329,406 to Flair, which discloses a capstan type cable drive comprising a cable drum about the outer surface of which several cable turns are wound and an endless belt which is carried by a plurality of driven sheaves arranged in a planetary fashion about the drum so that the belt defines a spiral or helical confining surface which imparts moving force to the cable during cable deployment. Such an arrangement will not accommodate xe2x80x9clumpyxe2x80x9d cable or sonar arrays as the sheaves are fixed relative to the cable drum and there is therefore a fixed clearance therebetween. Further, many cables and sonar arrays will only withstand a minimal degree of bending before suffering damage, such that the diameter of the drum would have to be relatively large and, together with the sheaves mounted around the drum, would occupy a large volume, which represents a distinct disadvantage in applications where space is at a premium, such as on a submarine.
Arrangements for maintaining a flexible member, such as an anchor rope in contact with a driven pulley are described in European Patent Application 0 176 463, and in U.S. Pat. No. 3,847,378. Both documents describe arrangements in which a belt is passed around a number of smaller pulleys located adjacent the larger driven pulley such that the belt presses the rope into contact with the driven pulley. However, in the disclosed arrangements the sole purpose of the belt is to ensure adequate frictional contact between the rope and the driven pulley.
UK Patent 1 368 157 discloses an arrangement in which a rope passes around a driven pulley and is clamped thereto by a series of clamping jaws mounted on an untensioned endless chain. The jaws positively engage notches on the driven pulley to ensure that the jaws follow the rope without any relative slipping. The jaws are urged into contact with the rope by spring-biassed pressure rollers.
It is among the objects of at least one aspect of the present invention to provide a drive assembly for a flexible elongate member such as a cable or sonar array having portions of different diameter.
According to the present invention there is provided a drive assembly for a flexible elongate member, the assembly comprising:
a support defining a convex arcuate support surface for engaging a flexible elongate member;
a tensioned flexible drive member opposing the convex support surface and defining a support portion for engaging the flexible elongate member;
first and second supports for the drive member, the supports being located on a chord of a curve whereby the drive member defines a concave arcuate support portion and tension in the drive member tends to bias the member to bear against the flexible elongate member.
The invention also relates to a method of applying a linear force to a flexible elongate member such as a cable or the like.
The manner in which the drive member is urged into contact with the flexible elongate member, that is by locating the drive member supports on a chord of a curve such that the tensioned drive member defines a concave arcuate support portion, with the tension in the drive member tending to bias the member to bear against the flexible elongate member, facilitates handling of xe2x80x9clumpyxe2x80x9d cables and the like; there is no requirement to provide support surfaces or rollers behind the drive member, and larger diameter portions of the cable are readily accommodated by flexing of the drive member.
The arrangement allows a linear force to be applied to a cable and the like without applying any significant radial or point loads thereto, as the force is applied to the cable over the length of the support portion. Thus, the assembly may be utilised to deploy or veer cable from a winch drum and to wind or haul cable onto a drum.
The assembly may be provided directly on a winch drum, or may be provided separately of the drum.
The invention has particular application in the deployment and retrieval of towed sonar arrays, in which the cable may be damaged if subject to high radial compressive forces. When deploying the array, the assembly may provide an initial tension to veer the cable from the winch drum. Then, once the drag on the array is sufficient to pull the cable from the drum, the assembly may run free. However, when the drag on the array reaches a level where the remaining coils of cable on the winch drum may be subject to a compressive force sufficient to damage the cable the assembly may provide drag on the cable to reduce the tension in the cable between the assembly first pulley and the winch drum. Further, the assembly may be utilised to haul the cable and retrieve the sonar array, allowing the cable to be wound onto the drum under minimal tension.
Preferably, the drive member supports comprise one or more pulleys. Most preferably, at least one of the pulleys is driven. Preferably also, at least one of the pulleys is mounted via biassing means to impart an initial tension in the flexible member.
Preferably also, the drive member is in the form of a belt, which may be toothed.
The support defining the convex arcuate support surface may be a pulley, preferably a relatively large diameter pulley. The convex support surface may be provided by a segment or arc of the pulley, preferably an arc of less than 270xc2x0, most preferably an arc of less than 180xc2x0, and in one preferred embodiment a 90xc2x0 arc.
In other embodiments the convex arcuate support surface may be provided by a belt passing around appropriate idler pulleys and supported at said surface by a low friction surface or multiple rollers. Alternatively, the support surface may be defined by a low friction surface or multiple rollers.
According to another aspect of the present invention there is provided an assembly for driving a wheel, the assembly comprising: a body; at least three pulleys mounted on the body; a flexible member extending around the pulleys; and means for driving the flexible member, two of the pulleys being locatable on a chord of a wheel to be driven such that tension in the flexible member tends to bias the member to bear on a portion of the circumference of a wheel located between said two of the pulleys.
The invention also relates to a method of driving a wheel.
The assembly may be provided in conjunction with a relatively large pulley wheel for providing drive for the pulley. Alternatively, the assembly may be utilised for driving a ground engaging wheel of a vehicle or aircraft to, for example, manoeuvre an aircraft on the deck of a ship. For such an application it is preferable that the said two of the pulleys are locatable relative to the wheel such that the flexible member extends around over half of the circumference of the wheel. of course this provides a greater degree of friction between the flexible member and the wheel and also facilitates securing the assembly on the wheel. With such an arrangement it is also desirable that at least one of said two pulleys is movably mounted to facilitate mounting and dismounting of the assembly from the wheel.
Preferably, one of the pulleys is driven and imparts a tension on the flexible member.
Preferably also, one of the pulleys is mounted on the body via biassing means to impart an initial tension in the flexible member.
Preferably also, the flexible member is in the form of a belt, which may be toothed.